This invention relates generally to the manufacture of nonwoven webs by meltblowing and/or or spunbond processes. In one aspect, it relates to an apparatus with interchangeable meltblowing and spunbond dies. In another aspect, the invention relates to a novel filament drawing or stretching device. In still another aspect, the invention relates to the in-line manufacture of spunbond-meltblown laminates.
Nonwoven fabrics have received commercial application in a variety of industries ranging from medical, diapers, filtration, apparel, draperies, absorption, environmental, to name but a few of such uses.
The term "nonwoven" refers to a sheet, web or batt of directionally or randomly oriented fibers, made by bonding or entangling the fibers through mechanical, thermal, or chemical means. Nonwoven fabrics exclude paper and products which are woven, knitted, tufted, or felted by wet milling. The fibers generally are man-made synthetics.
Although nonwovens may be made by a number of processes, the most popular processes currently in use are meltblowing and spunbond processes. Meltblowing is a process for the manufacture of a nonwoven fabric wherein a molten thermoplastic is extruded from a die tip to form a row of filaments (e.g. fibers). The fibers exiting from the die tip are contacted with converging sheets or jets of hot air to stretch or draw the fibers down to microsize diameter. The fibers are then deposited onto a collector in a random manner and form a nonwoven fabric.
The spunbond process involves the extrusion of continuous filaments through a spinneret. The extruded filaments are maintained apart and the desired orientation of the filaments are achieved by rotating the spinneret, by electrical charges, by controlled air streams, or by the speed of the collector. The filaments are collected on the collector and bonded by passing the layer of filaments through compacting roll and/or hot row calendering. Spunbonded webs generally have large average diameter (e.g. 12-100 microns, typically 15-50 microns) which are heavier and stiffer then meltblown fibers (e.g. 0.5-15 microns, typically 1-10 microns).
A paper presented at "Fiber Producer Conference 1983", in Greenville, S.C., entitled "Nonwoven Fabrics: Spunbonded and Meltblown Processes" describes the two processes in detail. The disclosures of this paper are incorporated herein by reference. It should be noted that the terms "fibers" and "filaments" when used in connection with nonwovens are interchangeable.
The meltblown fabrics are characterized as soft, porous with good hand, but are deficient in strength properties such as tensile strength and are not very wear resistant. On the other hand, the spunbond fabrics possess good strength properties and wear resistant but are not as flexible as meltblown fabrics.
It was discovered several years ago that the properties of the meltblown and spunbond fabrics could be combined by a laminate consisting of at least one layer of the meltblown web and at least one layer of the spunbond web. U.S. Pat. No. 4,041,203 discloses such a laminate. Over the years, improvements have been made in the laminate, the most popular being the so called S-M-S structure (spunbond-meltblown-spunbond) wherein a meltblown layer is flanked by two spunbond layers. The layers may be bonded together by compaction or by calendering, and exhibit outstanding strength properties, energy absorption, tensile strength, and tear resistance, and yet possess a soft, flexible feel or hand.
The S-M-S structures can be made by laminating the preformed webs or can be made by in-line operations wherein (a) spunbond filaments are laid on a moveable collector forming a first layer, (b) meltblown filaments are deposited on the first layer, and finally, (c) a second layer of spunbond filaments is deposited on top of the meltblown layer. The three layered structure then can be bonded together.
The in-line operation thus requires two spunbond apparatus and one meltblowing apparatus. The spunbond apparatus are large structures because of the long distance of the collector from the spinneret and are not readily adapted to other processes such as meltblowing. The meltblowing apparatus, on the other hand, employs a relatively short distance from the die to the collector and is not readily adapted to the spunbond process. The in-line apparatus thus is restricted to manufacturing only one type of laminate: the S-M-S laminate or portions thereof.